Various types of electric writeable media, commonly known as electric paper, exist in the prior art. One example of electric paper includes a polymer substrate and bichromal anisotropic particles, such as balls or cylinders that are in suspension with an enabling fluid and are one color, such as white, on one side and a different color, such as black, on the other. Examples of such electric paper are described in U.S. Pat. No. 5,723,204 to Stefik and U.S. Pat. No. 5,604,027 to Sheridon, each of which is incorporated herein by reference in its entirety. Under the influence of an electric field, the particles rotate so that either the white side or the black side is exposed.
Another type of electric writeable media is known as an electronic ink display, such as the one described in U.S. Pat. No. 6,518,949 to Drzaic, which is incorporated herein by reference. An electronic ink display includes at least one capsule filled with a plurality of particles, made of a material such as titania, and a dyed suspending fluid. When a direct-current electric field of an appropriate polarity is applied across the capsule, the particles move to a viewed surface of the display and scatter light. When the applied electric field is reversed, the particles move to the rear surface of the display and the viewed surface of the display then appears dark.
Yet another type of electric writeable media, also described in U.S. Pat. No. 6,518,949 to Drzaic, includes a first set of particles and a second set of particles in a capsule. The first set of particles and the second set of particles have contrasting optical properties, such as contrasting colors, and can have, for example, differing electrophoretic properties. The capsule also contains a substantially clear fluid. The capsule has electrodes disposed adjacent to it connected to a voltage source, which may provide an alternating-current field or a direct-current field to the capsule. Upon application of an electric field across the electrodes, the first set of particles moves toward a first electrode, while the second set of particles moves toward a second electrode. If the electric field is reversed, the first set of particles moves toward the second electrode and the second set of particles moves toward the first electrode. Other examples of writeable media include liquid crystal, non-encapsulated electrophoretic displays and other displays.
A general problem with electric writeable media is that it is difficult to quickly provide a proper electrical charge to each electrode on a substrate during writing and erasing operations. This is particularly the case where a secondary device is used to charge the electrodes (i.e., the electrodes are not connected via switches to a power source). Conventional secondary devices for providing charge to electrodes include wands, bars and styluses.
In operation, a wand or bar is charged to a known voltage. The wand or bar is then moved in relation to the electric writeable medium containing the electrodes. As the wand nears an electrode, the electrode is charged to a voltage by the resulting electric field. Wands and bars can inadvertently charge electrodes adjacent to the intended electrode because no direct contact point is established between the wand/bar and the intended electrode. As a result, a wand or bar may not produce a crisp image because electrodes are unintentionally charged.
A stylus can also be used to apply charge to an electric writeable medium. Typically, a human operator controls the stylus. The stylus is charged to a known voltage and is moved over the electric writeable medium. The stylus directly contacts the electrodes of the electric writeable medium and deposits a charge on the electrodes that it contacts. However, a stylus may imprecisely deposit charge due to human error. For example, the human operator may not precisely contact each intended electrode. As a result, the displayed image is likely to emulate handwriting. Even if a machine is used to precisely guide the stylus, the stylus has the disadvantage or being a point contact device. In other words, the stylus must contact each electrode that is to receive a charge. Thus, programming the entire electric writeable medium using a stylus can require a significant amount of time.
Therefore, a need exists for a method and system for making a device that precisely provides electrical charge to electrodes of an electric writeable medium.
A further need exists for a method of rapidly applying charge to a plurality of electrodes simultaneously using a secondary apparatus.
The invention described herein is directed to solving one or more of the above-listed problems.